Project Summary/Abstract The neocortex plays a critical role in complex cognitive tasks. At a mesoscopic level, similarities in the organization of the neocortex across species suggests that cortical processing and circuit motifs are well- preserved and stereotyped. This emphasizes the relevance and boosts motivation to study non-human mammals in the hopes of understanding cortical processing in the human brain. This project aims to investigate the roles of certain cell-types in neocortical circuitry. Specifically, the goal is to comprehensively characterize the cellular components involved in a sensory-processing and learning task in the mouse primary somatosensory cortex. Neurons in the somatosensory cortex will be probed to uncover three characteristics: anatomical identity based on their projection target, functional identity based on their activity patterns during a behavioral task, and molecular identity based on their transcriptome. Anatomical identity of neurons in the somatosensory cortex will be determined by retrograde labelling from target areas. Functional identity will be characterized by in vivo two-photon calcium imaging of neuronal activity during whisker-guided decision making tasks. Molecular identity will be visualized using ex vivo fluorescence in situ hybridization targeting mRNA transcripts informative of molecular cell-type. Drawing parallels between these three characterizations will result in comprehensive definitions of cells involved, with the expectation that homologies exist in the human brain. These experiments will identify key cellular components involved in sensory-processing, decision making, and learning, which will provide critical insight into how the brain performs complex computations.